1. Field of the Invention
This invention relates to a throttle device for an internal-combustion engine and, more particularly, to an electronically controlled throttle device which controls the opening and closing operation of a throttle valve by driving an electric actuator according to a control signal.
2. Description of Related Art
In an electronically controlled throttle device which controls an engine throttle valve by driving an electric actuator (e.g., a DC motor and a stepping motor), there has been known such a technology that the amount of initial opening (default opening) of the throttle valve is set larger than a full-closed position when an ignition switch is in off position (in other words, when no current is being supplied to the electric actuator).
Here, the full-closed position of the throttle valve is not meant by a position in which the intake air passage is full-closed; especially in a throttle device having-no bypass around the throttle valve and controlling the idling speed only by means of the throttle valve, the full-closed position is defined as a mechanically full-closed position and an electrically full-closed position which will be described below.
The mechanically full-closed position is the minimum opening position of the throttle valve defined by a stopper. The minimum opening is set at a position where the intake air passage is slightly opened from a full-closed position to thereby prevent the throttle valve from galling. The electrically full-closed position is the minimum opening position within the range of opening used in engine control, and is set, by the control of the electric actuator, at a position of a slightly wider opening than the mechanically full-closed position (e.g., about 1 deg. larger than the mechanically full-closed position).
In the electronically controlled throttle, the electrically full-closed position (the minimum opening for control) and the idle opening (an opening required for controlling the idle speed) do not necessarily agree. This is because the amount of opening of the throttle valve is controlled by a feed-back control system according to an idle speed detection signal in order to keep a target idle speed, and for this purpose the amount of opening is allowed to vary.
The full-open position has also a mechanically full-open position defined by the stopper and an electrically full-open position in which the throttle valve is opened to the maximum control amount of opening. The full-closed position stated herein includes the mechanically full-closed position and the electrically full-closed position as well. In normal control, the throttle valve is controlled within the range from the electrically full-closed position (the minimum opening for control) to the electrically full-open position (the maximum opening for control), so that a part of the throttle valve shaft will not hit on the stopper which determines the mechanically full-closed and full-open positions, when the throttle valve is being controlled to the minimum or maximum opening. Thus it becomes possible to protect the stopper and throttle components from mechanical fatigue, abrasion, and damage, and also to prevent galling to the stopper.
The default opening (i.e., the initial opening when the ignition switch is in off position) is set to the amount of opening of the throttle valve which is opened wider than the full-closed position (the mechanically full-closed position and the electrically full-closed position) (e.g., 4 to 13 deg. wider than the mechanically full-closed position).
The default opening is set from the reason for achieving the air flow rate necessary for fuel combustion for operation to be performed prior to engine warm-up at the time of engine starting (cold starting) without providing an auxiliary air passage (an air passage bypassing the throttle valve). During idling, the throttle valve is controlled towards decreasing the amount of opening from the default opening as the engine warm-up proceeds (in this case, however, the electrically full-closed position is the lower limit position).
Furthermore, the default opening is adopted to meet requirements for insuring self-running (limping home) in the event of a throttle control system trouble or insuring an intake air flow rate necessary for preventing an engine stop, and for preventing the throttle valve from being stuck with a viscous substance, ice, or other, on the inside wall of the throttle body.
As a conventional example of a default opening setting mechanism, various mechanisms have been proposed. A known prior art has been stated in, for example, Japanese Laid-Open No. Sho 63-150449 Patent Publication, U.S. Pat. No. 4,947,815 specification, Japanese Translation of PCT Application No. Hei 2-500677 corresponding to the US patent, Japanese Laid Open No. Sho 62-82238 Patent Publication and its corresponding U.S. Pat. No. 4,735,179 specification, Japanese Laid-Open No. Hei 10-89096 Patent Publication, and Japanese Laid Open No. Hei 10-131771 Patent Publication.
There are various types of default opening setting mechanisms, a typical type of which for example is as follows.
One type is of such a system that a default opening setting engagement element (a default lever) which is fitted on the throttle valve to enable the rotation of the engagement element on the throttle valve shaft is engaged via a spring with an element secured on the throttle valve, thereby allowing the default lever to turn together with the throttle valve shaft between the range from the default opening position to the valve full-open position. When the ignition switch is in off position, the default lever is held in contact with the default stopper, to thereby hold the throttle valve opening at the default opening. To close the throttle valve to the default opening or less, the default lever is disengaged from the throttle valve shaft to allow the throttle valve shaft to rotate independently against a spring force towards closing the throttle valve.
Another type is of such a system that, reversely to the above-described system, the default lever and the throttle valve shaft are turned together from the throttle valve full-close position to the default opening position. When the ignition switch is off, the default lever is held in contact with the default stopper to hold the throttle valve opening at the default opening. When the throttle valve is opened over the throttle opening, the default lever is disengaged from the throttle valve shaft, to allow the throttle valve shaft to turn towards opening independently against the spring force.
The electronically controlled throttle device can perform more accurately the air flow rate control suitable for the operation of the internal-combustion engine than a mechanical throttle device which transmits the amount of depression of the accelerator pedal to the throttle valve shaft through an accelerator cable. The component count is increased to provide an electric actuator, a default opening setting mechanism, and a throttle sensor. Therefore, downsizing, weight reduction and simplification, rationalization of fabrication and adjustment jobs, and further improvement in operation stability and accuracy of the throttle body, are demanded.
To solve the above-described problem, therefore, it is an object of the invention to realize the downsizing, weight reduction and simplification of the throttle body equipped with an electric actuator, a gear mechanism and a default opening setting mechanism, the rationalization of fabrication and adjustment jobs, and further improvement in operation stability and accuracy.
This invention basically has the following constitution.
The first aspect of the invention pertains to the throttle device for an internal-combustion engine which is driven by an electric actuator to open and close the throttle valve to thereby control the amount of intake air aspirated by the internal-combustion engine. In the throttle device, there are formed, on one surface of the side wall of the throttle body, a reduction gear mechanism mounting space which transmits to the throttle valve shaft the power of the electric actuator, and a frame for mounting a gear cover formed to define the space for mounting the reduction gear mechanism. The frame is built lower than the mounting height of the gear mounted on one end of the throttle valve shaft. On the frame is attached the gear cover for covering reduction gear mechanism mounting space.
According to the above-described constitution, the reduction gear mechanism mounting space is covered with a gear cover, which covers most of the mounting space, in place of a gearcase and a gear cover mounted on the side wall of a conventional throttle body. In this sense, the gear cover plays a role of the gearcase. Unlike the conventional type, therefore, the throttle body itself is not needed to be formed integrally with a gearcase having a relatively large volume. A gear cover made of a synthetic resin should be increased in the volume; generally, therefore, it is possible to reduce the size and weight of the metal throttle body formed by mold casting.
The second aspect of the invention pertains to the throttle device of the internal-combustion engine having the default opening setting mechanism to hold the amount of opening of the throttle valve at a specific opening (the default opening) which is larger than the full-close position when the electric actuator is off.
In this throttle device, the stopper for defining the default opening position and the stopper for defining the mechanically full-closed position of the throttle valve are comprised of adjusting screws. These stoppers are so juxtaposed as to enable adjustment of their position in the same direction.
According to the above-described constitution, it is possible to freely adjust the default opening and the mechanical full-closed position of the throttle valve. Besides, since the adjusting screw of the default opening stopper (the default stopper) and the adjusting screw of the full-closed stopper are juxtaposed to allow position adjustment from the same direction, it is possible to drill screw holes for these stoppers (screws) in the same direction, and moreover to perform the adjustment of the stopper positions in close positions from the same direction, thereby enabling simplification of adjustment jobs.
The third aspect of the invention is application of the first and second aspects of the invention, pertaining to the throttle device of the internal-combustion engine. In the aspect, the full-closed stopper stops the reduction gear (the final gear) fixedly attached on the throttle valve shaft, to thereby define the mechanical full-closed position, while the default stopper stops an engagement element for setting the default opening (this engagement element is a default lever freely fitted on the throttle valve shaft to enable rotation of the shaft and engaged with the final gear through a spring), thus defining the default opening.
In the throttle device, there are formed, on one surface of the side wall of the throttle body, a space for mounting a reduction gear mechanism which transmits to the throttle valve shaft the power of the electric actuator, and a frame for mounting a gear cover formed to define the space for mounting the reduction gear. The frame is built lower than the mounting height of the final gear. In the position covered by the gear cover, there is provided a projecting portion, which is higher than the frame, for mounting the full-closed stopper. Mounted on this projecting portion is the full-closed stopper, at the same mounting height as the final gear of the reduction gear. On the other hand, the default stopper is juxtaposed with the full-closed stopper at the position of the said engagement element (the default lever) which is located at the lower level than the said frame.
According to the above-described constitution, the space for mounting the reduction gear mechanism is covered almost by the gear cover like in the first aspect of the invention. It is, therefore, possible to reduce the size and weight of the metal throttle body.
The final gear of the reduction gear protrudes out of the gear cover mounting frame on the throttle body side wall; therefore, the final gear can not be stopped if the full-closed stopper is provided on this frame. In the aspect, there is provided a projecting portion for mounting the full-closed stopper which stops the final gear. The projecting portion protrudes high over the frame. On this projecting portion the full-closed stopper is arranged at the same mounting height as the final gear.
According to this arrangement, it is possible to stop the final gear by the full-closed stopper if the gear cover mounting frame is built low.
The fourth aspect of the invention pertains to a throttle device for an internal-combustion engine having the default opening setting mechanism.
The throttle valve shaft protrudes out at one end from the bearing boss formed on the throttle body side wall, and the final gear of the reduction gear for transmitting the power of the electric actuator is fixedly attached on the one end of the throttle valve shaft. Between the final gear and the bearing boss, the engagement element (the default lever) of the default opening setting mechanism capable of engaging with the final gear is rotatable with respect to the throttle valve shaft.
A return spring is arranged around the bearing boss for exerting the spring force to the throttle valve in the direction the throttle valve is closed. The return spring engages at one end with the default lever; and between the default lever and the final gear there is mounted a spring (the default spring) for attracting the default lever and the final gear towards mutual engagement.
A throttle valve shaft insertion boss is formed only on the surface side (one surface side) of the final gear which receives the default spring. The default lever also has a throttle valve shaft insertion boss formed correspondingly to the final gear boss. And around these bosses the default spring is mounted.
According to the above-described constitution, the return spring and the default spring can be installed in a free space inevitably formed around each boss. That is, rational utilization of space is realized. Moreover, since the boss of the final gear of the reduction gear is protrusively formed on one side only, the amount of projection of the boss (the length of boss axis) protruding out from one side of the final gear can be made longer than the amount of projection of the boss on one side of double-sided bosses (bosses protruded on both sides of the final gear). Therefore, it becomes possible to provide the default opening setting mechanism with a spring mounting space without wasted space while realizing a downsized throttle device.
The fifth aspect of the invention pertains to a throttle device for an internal-combustion engine having the default opening setting mechanism.
In the throttle device, the final gear of the reduction gear which transmits the power of the electric actuator is secured on one end of the throttle valve shaft, and the engagement element (the default lever) of the default opening setting mechanism is relatively rotatably fitted on the throttle valve shaft.
Between the default lever and the final gear there is installed a spring (a default spring) for setting the default opening which pulls the default lever and the final gear towards mutual engagement. The default spring is characterized by the spring stop mechanism that the default spring is supported by the default lever and the final gear.
According to the above-described constitution, the default lever and the final gear of the reduction gear serve also as a default spring bracket, thereby enabling simplification of component parts.
It is, therefore, proposed as an example of application that at least a portion forming the boss and a portion receiving the default spring of the default lever are made of a synthetic resin.
According to the above-described constitution, since the synthetic resin is of a less coefficient of friction than a metal member, friction between the default spring and a member (the spring stop portion in the default lever, and the boss portion) which contacts the default spring will be decreased to reduce a burden on the motor if the default spring is twisted by the relative rotation of the default lever and the final gear, thereby achieving smooth movement of the throttle valve driven by the motor and a decreased motor power consumption during operation.
Furthermore, the use of the return spring and the default spring coated for reducing a coefficient of friction can further decrease its friction with its mating member in case of distortion of the spring.
The sixth aspect of the invention pertains to a throttle device for an internal-combustion engine having the default opening setting mechanism.
In the throttle device, the engagement element (the default lever) for setting the default opening is fitted on one end of the throttle valve shaft in such a manner that the engagement element can rotate in relation to the throttle valve shaft.
On both sides of the engagement element, the return spring exerting a spring force to turn the throttle valve towards closing and the default opening setting spring (the default spring) exerting the spring force from the full-close position of the throttle valve to the default opening side are oppositely arranged in the direction of the throttle valve shaft. These springs which are torsion coil springs seat on both sides of the engagement element serve as spring stopper, thereby retaining these springs at one end. These springs differ in coil diameter and are axially compressed when installed. Furthermore, the compressive stress F of the spring of large coil diameter is made greater than the compressive stress f of the spring of small coil diameter. The compressive stress of the spring stated above is spring rebound which occurs when the spring is compressed.
The throttle valve shaft is required to be disengaged from the engagement element for setting the default opening and to turn independently when turned within a specific range of throttle valve opening (e.g., from the default opening to the electrically full-closed position, or from the default opening to the electrically full-open position of the throttle valve), and accordingly the engagement element for setting the default opening is attached loose-fit on the throttle valve shaft so that the engagement element can rotate with respect to the throttle valve shaft.
Therefore, there exists a clearance between the outer periphery of the throttle valve shaft and the engagement element for setting the default opening. Therefore, the engagement element for setting the default opening will vary (displace) with vibrations if in an unstable state. If the engagement element for setting the default opening is held by the compressive force of the coil return spring and the default spring, and if the compressive stresses of these springs are equal, and also if these springs get out of balance, the engagement element for setting the default opening is liable to vibrate, becoming unstable. Consequently, the default opening will vary, and no smooth operation of the engagement element can be expected.
In the present invention, to cope with this problem, it is necessary to increase the compressive stress F of the return spring or the default spring having a large coil diameter than the compressive stress f of the spring having a small coil diameter. The compressive force F thus increased can overcome the compressive force f, and unidirectionally press the engagement element in a stable state in a position close to the outside diameter, thereby preventing the engagement element for setting the default opening from displacing to enable to maintain a proper condition and accordingly preventing above-described trouble.
The seventh aspect of the invention pertains to a throttle device for an internal-combustion engine, wherein the throttle device is provided with a reduction gear for transmitting the power of the electric actuator to the throttle valve shaft; the final gear of the reduction gear is pressed in and fixed on one end side protruding out of the side wall surface of the throttle body of the throttle valve shaft; and the final gear thus pressed in and fixed can contact the stopper for defining the mechanical full-closed position of the throttle valve, by driving the electric actuator.
According to the above-described constitution, since the final gear of the reduction gear serves also as a defining element on the movable side which restricts the mechanical full-closed position and also the defining element (the final gear) is pressed in and fixed on the throttle valve shaft, the reduction gear position is constantly held in a fixed relation with the throttle valve shaft even in case of a shock caused by the contact of the reduction gear with the full-closed stopper. Therefore, the throttle valve opening set with reference to the mechanically full-closed position will not vary, thus doing much towards keeping a control accuracy.
The eighth aspect of the invention pertains to a throttle device for an internal-combustion engine which is driven by an electric actuator to open and close the throttle valve to control the amount of intake air being aspirated by the internal-combustion engine.
In the throttle device, the motor used as the electric actuator has a yoke forming a motor housing. The yoke is provided with two opposite flat surfaces. The motor casing containing the motor has flat opposite inner surfaces formed to the contour of the motor housing, and is mounted on the side wall of the throttle body, intersecting the line orthogonal with the throttle valve shaft. Of the opposite flat inner surfaces of the motor casing, all or most part of one inner surface makes up the outside wall surface of the intake air passage downstream of the idle opening position for throttle valve control (e.g., downstream of the electrically full-closed position for throttle valve control).
According to the above-described constitution, using the flat motor housing and accordingly the flat motor casing can contribute to the downsizing of the throttle body. Besides, since one of the flat inner surfaces of the motor casing makes up the outside wall surface of the intake air passage downstream of the idle opening position for throttle valve control, the motor casing is most efficiently cooled by the adiabatic expansion of the intake air occurring downstream immediately after passing the throttle valve during an idle turn even if the intake air flow rate is little like during idle turn. Therefore, The cooling of the motor casing interior and the heat dissipation of the motor housing can be improved, thereby contributing to achieving a higher motor cooling effect.
The ninth aspect of the invention pertains to a throttle device for an internal-combustion engine, in which the motor casing for containing the motor, as previously stated, has opposite flat inner surfaces formed to the contour of the motor housing, and is installed on the side wall of the throttle body, intersecting the line orthogonal with the throttle valve shaft. Of the opposite flat inner surfaces of the motor casing, one inner surface is formed lower than the surrounding outside wall surface of the intake passage.
According to the above-described constitution, the motor casing wall adjacent to the intake passage is decreased in thickness to bring the inner surface of the motor casing closer to the intake passage side, thereby enabling to efficiently benefit from the cooling effect of the intake air passing through the intake air passage.
Other objects and advantages of the invention will become apparent upon reading the detailed description and upon reference to the accompanying drawings.